<!doctype html>
<html>
<head>
<meta charset="utf-8">
<title>무제 문서</title>

</head>

<body>
<form name=form>
 <select name=dong onchange=alert(this.value)>
 </select>
</form>

<script>
function aaa(){
 tid=new Array(document.form.dong.options.length);
 for(i=0;i<document.form.dong.options.length;i++){
  document.form.dong.options[i]=null;
 }
 document.form.dong.options[0]=new Option('none','번지수에서');
 document.form.dong.options[1]=new Option('first','1번');
 document.form.dong.options[2]=new Option('second','2번');
}
function bbb(){
 document.form.dong.options[0]=new Option('none','층수에서');
 document.form.dong.options[1]=new Option('first','1층');
 document.form.dong.options[2]=new Option('second','2층');
 document.form.dong.options[3]=new Option('third','3층');
 document.form.dong.options[4]=new Option('fourth','4층');
}
window.onload=function(){
 bbb();
 aaa();
}
</script>
</body>
</html>
